Method of and means for forming bellows



Nov. 17, 1959 PETERS 2,912,951

; METHOD OF AND MEANS 0R FORMING BELLOWS Original Filed Deo 15, 1950VE/VTOR. Melvlll .Pefers ATTORNEYS United States p t lVIETHOD OF ANDMEANS FOR FORMING BELLOWS Melville F. Peters, Livingston, NJ.

Original .application December 13, 1950, Serial No. 200,561, now PatentNo. 2,761,206, dated September 4, 1956. Divided and this applicationJuly 5, 1956, Serial No. 595,998

4 Claims. (Cl. 113116) This invention provides a method of formingcurved surfaces for fluid seals and means to secure the curved surfacestogether to form bellows.

This application is a division of an application, Serial No. 200,561,filed December 13, 1950, now Patent No. 2,761,206, issued September 4,1956, by Melville F Peters, and entitled Method of and Means for FormingBellows.

As hereinafter used, the term curvature of surfaces of minimum stressfor bellows elements shall be understood to mean the surface formed whena flexible member or membrane is secured or supported by two cylindricalelements and a fluid pressure or its equivalent applied to one side ofthe membrane, so that the unsupported and unguided area will deform intoa curved surface and if the pressure is great enough to exceed theelastic limit of the membrane in the unsupported area, the deformationwill continue until the stresses in the membrane are reduced to theyield point.

If the curved surface of bellows elements are formed at a pressure nPand 11:1, the stresses in the elements in the rest position whensubjected to a pressure P, is approximately equal to the yield strengthof the material and if the bellows is oscillated through an amplitude of:X when subjected to the forming pressure, the stresses caused in themembrane by the oscillations must be algebraically added to the yieldstrength of the material. During the life of the bellows the curvatureof the surfaces will change so as to accommodate itself to the greateststress, but unless the bellows is subjected to conditions which willincrease the curvature of the surface, the flexing life of the bellowswill be short.

If the formed element is annealed and subjected to the forming pressure,there will be a small increase in curvatures because the yield point ofthe material is slightly lower in the annealed condition. This processof subjecting the membrane to the forming pressure and annealing may berepeated many times with a small increase in curvature, but at adecreasing rate of increasing curvature for each cycle. The samelimiting curvature could have been obtained in one operation by makingit slightly greater than 1.

If n is greater than 1 and, for the sake of illustration, is equal to10, the stresses in the annealed membrane will be approximately tenpercent of the yield strength, since the stress S in a membranesubjected to a pressure P, is S=KP, where K is a complicated function ofthe physical dimensions and properties of the membrane. If the membraneis oscillated through an amplitude '-X, the stresses developed in themembrane will be added algebraically to ten percent of the yieldstrength, so that Patented Nov. 17, 1959 by controlling the amplitude ofoscillation the annealed membranes will operate within the elasticlimit.

The surface formed by the pressure nP is not actually the surface ofminimum stress for a pressure nP, because the deformation of themembrane stopped when the yield point of the material was reached, andtherefore it difiers from the real curvature of a surface having minimumstress by an amount which is proportional to the modulus of elasticityof the membrane material, and approaches the true shape as the modulusof elasticity approaches zero. The true surface shape for each depth ofcurvature may be photographed or observed by applying fluid pressure toa soap or rubber film secured by its edges to appropriate forms. Thesurface shape or curvature may then be transferred to a die and flexiblemember stamped in the conventional manner.

It is an object of this invention to eliminate this procedure byproviding a method for forming the curvature of membrane surfacesbounded by two other surfaces or areas, by applying a uniform pressureof n? over the confined surface, and after securing the membranestogether by means of the bounding areas to form a bellows, to limit theworking pressure of the bellows to a fluid pressure P. For all practicalpurposes the fiber stress in the curved surface of a membrane formedwith n greater than one, will be the same as the fiber stress in amembrane with the curvature copied from the soap film, when bothsurfaces have the same depth of curvature and the working pressure doesnot exceed P. The curvature of the surface is controlled by the formingfluid pressure nP, so that by assigning a series of values to 111, afamily of surfaces having minimum stress are obtained with the samefixture, and the forming fluid pressure required is determined by theworking pressure P, the yield strength of the membrane material and theconvexity or concavity of the surface subjected to the working pressurein the bellows.

Another object of the invention is to provide a method for forming thecurvature of membrane surfaces by applying a fluid pressure of nP overan unsupported portion of the membrane until equilibrium is establishedbetween the forming pressure, the yield strength of the material and thethickness of the membrane, so that adjustment in curvature fornon-uniformity of material thickness and composition is realized duringthe forming process, and two areas which serve as supports for themembrane during the forming process, are means for securing themembranes together to form a bellows.

It is a further object of the invention to provide a method of formingthe curved surface with a fixture that changes the width of the curvedsurface throughout its perimeter, so that the amount of inertia of theformed surface is not constant throughout the perimeter, and therebyprovide means for limiting the fiber stress in the regions of thesurface where the ambient conditions lead to great shearing forces andlarge bending moments.

It is an object of the invention to provide a method of forming thecurved surface with a fixture that permits changes in the width of oneor both of the two bounding areas throughout the perimeter and therebyprovide means for limiting the fiber stress in the regions of thesurface where the ambient conditions lead to great shearing forces andlarge bending moments.

It is also an object of the invention to provide a method for formingdiaphragms by supporting the outer area of a membrance and applying afluid pressure to the central portion, thus causing the unsupported andunguided portion to deform until equilibrium is reached between thecurvature of the deformed surface and the forming pressure.

It is an object of the invention to provide a method for formingsurfaces of curvature of minimum stress by applying a greater pressurethan the forming pressure nP and limiting the deformation to that of amembrane subjected to a forming pressure nP, by means of a limitingdevice.

Other objects and advantages of this invention relating to thearrangement and operation of the forming elements and economies ofmanufacture will be apparent to those skiiled in the art uponconsideration of the description, drawings and appended claims.

The invention consists of the construction, combination and arrangementsof parts, as herein illustrated, described and claimed.

In the accompanying drawings, forming a part hereof is illustrated oneform of embodiment of the invention, and in which:

Figure 1 is a cross sectional view of the curvature of a surface havingminimum stress and the arc of a circle shown in dashed linessuperimposed on a portion thereof.

Figure 2 is a top plan view of a view of a blank from which the bellowselement is formed in accordance with the present invention.

Figure 3 is a top plan view of the bellows element after its formationin accordance with the present invention.

Figure 4 is a cross sectional view taken on line 4-4 in Figure 2.

Figure 5 is a cross sectional view taken on line 55 in Figure 3.

Figure 6 is a fragmentary view in cross section showing the fixture bywhich the membrane discs are stressed with a portion of said disctherein, prior to the application of pressure.

Figure 7 is a view similar to Figure 6 showing the formed membranewithin the fixture.

Figure 8 is a vertical section taken through a portion of a bellowsassembly composed of a plurality of discs made in accordance with thepresent invention, Welded at their alternate edges to form a rigid fluidtight structure.

Referring to the drawings and particularly to Figures 1 and 2, 10indicates a flat somewhat washer shaped blank stamped from some suitablemetal such as copper, stainless steel or the like which blank has thegenerally cross sectional shape illustrated in Figure 4. The blank 10 isinserted within a fixture 11, best shown in Figures 6 and 7. The fixture11 is shaped to conform substantially to the blank 1% and comprises anupper member 12 and a lower member 13. The upper member 12 is providedwith downwardly extending jaw portions 14 which are adapted to bear uponthe upper surface of the blank H1. The lower member 13 is formed withupwardly disposed jaw portions 15 adapted to bear upon the under side ofthe blank 10. The jaw portion members 14, 15, grasp the blank 1t),therebetween at a point spaced from the inner and outer periphery ofsaid blank. A suitable opening 16 is provided in the lower member 13 forthe introduction therethrough of fluid under pressure. The upper member12 may be formed with a vent 17 leading from the interior of the member12 to the atmosphere. The jaws 14, 15, may be provided with holding andsealing surfaces 18.

When it is desired to form a membrane in accordance with the presentinvention the membrane blank 10 is held and sea ed between the jaws 14,15 and the forming pressure applied until equilibrium is establishedbetween the curvature of the surface, the yield strength of the matrial,and the forming pressure nP. The process can be carried out by two ormore steps by applying the pressure nP, annealing and then continuingthe process by again applying the pressure nP, to form the blank with acurvature of surface of minimum stress. This curvature is illustrated inFigure 1, at '19.

An alternate procedure in applying the forming pressure is to apply apressure greater than the forming pressure nP and have a conventionaltriggering device (not shown) release the pressure at the instant theforming of the surface is complete.

Referring to Figure 1, the curvature 19 is a cross sectional view of asurface having the defined surface curvature of minimum stress and isformed by subjecting an unsupported portion of the membrane 10 to afluid pressure which stresses the membrane beyond the yield point of thematerial. A cross sectional view of an arc of a clrclehavin-g the samedepth of curvature as 19, has been superimposed upon the showing ofFigure 1, and appears as the dotted line 29. The margins or edges bywhich the blank 10 is supported during the forming operation areindicated at '21 and 22 in Figure l. These-margins 21, 22, provide meansfor securing the curved members together to form a bellows as indicatedin Figure 8.

In the formation of a bellows 23, shown in Figure 8, the curved surfaces19, are prevented from touching during compression of the bellows 23 byforming the adjacent margins 21, 22, on the assembled membranes ofdifferent sizes.

Referring again to Figures 6 and 7, the fixtures 11, with chambers 24,25, therein and jaw members 14, 15, are shaped to form bellows elementsor sections of bellows elements, which sections may be secured togetherto form elements. These formed elements consist of surfaces having theminimum stress bounded by areas or edges 21, 22, and the separation ofjaw elements 14, 15, can be increased or decreased throughout theirperimeter so as to increase or decrease the width of the curved surface19 throughout the perimeter and thereby increase or decrease the momentof inertia along the perimeter to compensate for the unequaldistribution of the shearing forces and bending moments induced in theelements, and thus meet the fiber stress in the element within theelasticity throughout. The width of the margins 21, 22, can be increasedor decreased by increasing or decreasing the width of the unformedmembrane without placing limitations upon the separation of the jaws 14,15, so that the width of the two areas 21, 22, can be changed throughouttheir perimeter to compensate for the unequal distribution of shearingforces and bending moments induced in the elements.

Having thus fully described the invention, what is claimed as new anddesired to be secured by Letters Patent of the United States, is:

1. A device for forming bellows membranes from flat washer-shaped blankscomprising complementary upper and lower forming members, said uppermember having downwardly extending spaced annular jaws and anintermediate connecting portion with a vent hole therein between saidjaws defining a chamber for receiving the unconfined formed portion ofthe blank, said lower member having upwardly extending spaced annularjaws and an intermediate portion with a fluid introducing openingtherein connecting said jaws and defining a chamber for applying fluidunder pressure to the bottom side of the unsupported portion of saidblank to form the same.

2. A device for forming bellows membranes according to claim 1 in whichthe upper and lower annular jaws are provided with fluid sealingsurfaces to prevent the passage of fluid from the chambers between thejaws and the blank during the forming operation.

3. The method of forming bellows membranes comprising, the steps ofstamping a substantially washershaped blank from a suitable metal,grasping and supporting the stamped blank on both sides but only inareas adjacent its peripheral edges, and thereafter subjecting one sideof the unsupported portion of the blank to direct contact of fluidpressure of a magnitude to stress the said unsupported portion of theblank material beyond its elastic limit, by means of a pressure applyingchamber surrounding said side of said unsupported portion of said blank.

4. The method of forming bellows membranes according to claim 3 in whichthe blank is subjected to successive fluid stresses upon the sameunsupported side and annealed after each of said stress operations.

References Cited in the file of this patent UNITED STATES PATENTS Cutleret a1. Nov. 10, 1925 Seibt Apr. 26, 1927 Gulick June 10, 1930 FOREIGNPATENTS Germany Sept. 5, 1928 Great Britain Nov. 13, 1934

